As described in U.S. Pat. No. 6,229,054, cardanol is a meta-substituted phenol obtained by treating cashew nut shell liquid (CNSL). CNSL consists primarily of anacardic acid which is decarboxylated when heated, yielding cardanol. As shown in FIG. 1, cardanol is a phenol with a meta-substituted 15 carbon unsaturated aliphatic side chain. The aliphatic side chain may have either one, two or three carbon double bonds. Cardanol has been used as a base material to form, for example, hydroxyalkylated cardanol used as a modifier in coatings, adhesives, sealants, rubbers, plastics, elastomers and inks.
Fouling of ship bottoms and other marine structures by organisms such as barnacles, tube worms and algae is a problem which has existed from ancient times to the present. It has become routine practice to prevent these organisms from attaching to ship bottoms and other marine structures by coating exposed surfaces with an anti-fouling coating or paint.
Beginning in the mid-1800's, toxicants were included in paints for ship bottoms and other marine structures. Copper compounds, such as copper sulfate and cuprous oxide, were among the first toxicants used in anti-fouling paints. Over the years, a variety of toxicants have been used, including tin, arsenic, mercury and oxides of zinc, lead and mercury. More recently, organotins such as tributyltins, have been used in anti-fouling marine paints.
Prevention of fouling by use of toxic paints requires maintaining a lethal concentration of the toxicant in the water immediately adjacent to the surface being protected. There are at least two disadvantages to this approach: (1) the leaching action of the toxicant from the paint will eventually exhaust the supply of the toxicant and the paint will no longer be effective, and (2) the toxicants are environmentally undesirable and can be a major source of pollution in busy harbors and waterways.
One solution to these problems has been the development of so-called foulant release coatings. These coatings are often silicone based materials to which foulant organisms do not adhere. One disadvantage of these coatings is that it can be likewise difficult to adhere the material to the surface being protected. While this can sometimes be addressed in part by more extensive preparation procedures, this can increase the time and expense involved in coating a surface.
Another approach which is intended to address, at least in part, the problem of adherence of the coating to the surface is described in U.S. Pat. No. 5,593,732. This patent describes an anti-fouling coating system comprised of two layers. A solid bonding layer is bonded to the substrate, and a solid release layer is bonded to the bonding layer. This system requires multiple components and the application of two layers, increasing the time and expense associated with application of the coating.
Accordingly, there is a need for an improved anti-fouling coating which can be applied to marine structures, such as ship bottoms, economically, and that prevents marine organisms from bonding to the surface of the marine structure.